In U.S. Pat. No. 6,341,621, a fluid operated device or tool 10 is shown, which includes a valve structure 36 that functions as a combined over-pressure relief and pressure release mechanism. FIG. 1 shows the conventional valve structure 36′ similar to that of the above-mentioned patent. In the normal course of operation, fluid pressure in the tool 10 continues to increase by action of a pump piston 20 that imparts increased force on a ram piston 28. When pressure in a drive chamber C reaches a pre-determined pressure as regulated by spring 38, ball valve 40 disengages from its seat, thus permitting fluid flow through opening 42. Fluid moves into a bulkhead chamber 43 until the pressure in the drive chamber C returns to the pre-determined maximum pressure. Fluid entering chamber 43 is distributed to a piston reservoir chamber E through conduit 44 and into chamber A via a conduit (not shown). This overpressure relief mechanism prevents the tool 10 from becoming too aggressive for its work and provides the user a cautionary measure of safety.
Once the tool 10 has performed its work, valve structure 36′ becomes the mechanism for releasing and resetting the tool 10. Over-travel of the pump piston 20 away from the bulkhead 12 beyond its normal pumping range will cause the valve structure 36′ to travel to the right in FIG. 1. Travel of the valve structure 36′ can be controlled via adjustment nut 54. Travel of the valve structure 36′ unseats ball valve 40 permitting fluid in drive chamber C to communicate with accumulator chamber A through a conduit (not shown), and through barrier valve 60 to communicate with ram reservoir chamber B, and through conduit 44 to communicate with the piston reservoir chamber E that communicates with pumping chamber D. While in this mode, ram 28 may be retracted into the tool 10 by hand or some other external force. Once the tool 10 has been reset, the pump piston is released from its over-traveled position and spring 38 will reseat valve 40.
Although the valve structure 36′ works well for its intended purpose, the valve structure can be improved to modulate the pressure in the drive chamber C.
Thus, there is a need to provide a valve structure in a fluid operated device to provide modulation of the device.